1. Field of the Invention
The present invention relates generally to a system for restoring a controlled unit from an abnormal condition. More specifically, the present invention relates to a system for controlling operations of a controlled actuating unit, wherein the operations of the controlled actuating unit are monitored and diagnosed, and further restored when abnormality is detected. The present invention is particularly applicable to the sequence control of the actuating unit performed by a sequence controller including a programmable controller, a relay circuit, a robot controller and a numeric controller.
2. Description of the Prior Art
Various diagnostic systems for controlled actuating units are known as disclosed in references such as Japanese First (unexamined) Patent Publication No. 1-48206 and Japanese Second (examined) Patent Publication No. 1-52762.
Japanese First Patent Publication No. 1-248206 discloses a programmable controller. A sequence program to be executed by the controller is formed by a plurality of routines, each having sequence steps. A timer is provided for checking whether the routine proceeds from one step to a next step within a preset maximum time. An abnormal condition is determined when the timer counts up the preset maximum time. When the abnormal condition is determined, all transition conditions necessary for proceeding to the next step with an indication of the unsatisfied transition condition are stored in a data memory, which can be displayed on a display screen.
Japanese Second Patent Publication No. 1-52762 discloses a programmable controller including a calculation mode and a run mode. In the calculation mode, maximum and minimum ON times or OFF times of each output relay are derived by operating a controlled unit. In the run mode, ON times or OFF times of each output relay are derived by actually operating the controlled unit, and an abnormal condition is determined when the derived ON time or OFF time of each output relay exceeds the corresponding maximum or minimum ON or OFF time.
However, though the occurrence of the abnormality can be known in both publications and all the transition conditions with the unsatisfied transition condition can be known in Japanese First Patent Publication No. 1-248206, the restoring operation for all abnormal conditions should be manually performed by the operator. This is troublesome to the operator and deteriorates the operation efficiency.
Further, when a new abnormal condition which is not predictable beforehand occurs, since no indication of a required transition condition can be shown to the operator, it is difficult for normal operators to deal with that abnormality. Specifically, after a well experienced operator has manually restored the system from the particular new abnormality with his own knowledge, no other operators can share what the well experienced operator has learned. Further, if such abnormality occurs repeatedly, the well experienced operator has to perform the same or similar manual operations repeatedly. This possibly deteriorates the operation efficiency.
On the other hand, though it is theoretically possible to include all predictable abnormal conditions, i.e. all predictable transition conditions in the sequence program, such an inclusion requires a great deal of efforts and is not practical. In practice, the abnormality is so irregular that it is extremely difficult to make the sequence program for predicting all possible abnormal conditions. Further, since abnormal conditions actually generated form only a part, dealing with all predictable abnormality is not practical, but is wasteful.